Compositions for and methods of improving adhesion of plated metal on plastic substrates

ABSTRACT

A method of and composition for promoting adhesion between plated metal and a plastic substrate, in which the active agent is provided in finely divided dispersed or colloidal form in an aqueous emulsion. The active agents are any of a group of low molecular weight organic unsaturated compounds of the fatty acid type, and more especially of the group of naturally occurring products such as linseed, tall, tung and castor oils, turpentine and similar wood rosins. These, when dispersed in water to provide stable emulsions, are used as a pretreatment bath for plastic substrates, prior to plating of the substrate, in order to promote the formation of a stronger bond between the metal plate and substrate.

United States Patent 1191 Grunwald et al.

111 3,716,392 [451 *Feb. 13, 1973 COMPOSITIONS FOR AND METHODS OFIMPROVING ADHESION 0F PLATED METAL ON PLASTIC SUBSTRATES Inventors, JohnJ. Grunwald,'New Haven; Eu-' gene D. DOttavio, Thomaston, both of Conn.

Assigneez- MacDermid Incorporated, Waterbury, Conn.

Notice: 1 The portion of the term of this patent subsequent to May 18,1988, has been disclaimed.

Filed: May 11, 1970 Appl.'No.: 48,713

Related US. Application Data Division of Ser. No. 645,901, June 14,1967, Pat. No. 3,579,365.

US. Cl ..1'l7/47 A,'l17/130 E, 117/160 R, l17/l38.8 E, 204/30 Int. Cl...B01j 13/00, B44d G08h 9/00 Field of Search 106/265, 1; 117/47 R, 47 A,

' [56] References Cited UNITED STATES PATENTS 3,556,955 1/1971 Ancker eta1 ..117/47 A 3,574,700 4/1971 Sahely ..117/47 A 3,501,332 3/1970Buckman ..1 17/47 A Primary Examiner william D. Martin AssistantExqminer-William R. Trenor AttorneySteward & Steward, Roy F. Steward,Merrill F .-.Steward and Donald T. Steward 57 ABSTRACT prior to platingof the substrate, in order to promote the formation of a stronger bondbetween the metal plate and substrate.

9 Claims, No Drawings COM POSITIONS FOR AND METHODS OF lMPROVlNGADHESION OF'PLATED METAL ON PLASTIC SUBSTRATES This application is adivision of copending application Ser. No. 654,901, filed June 14, 1967,now U.S. Pat. No. 3,5 79,365.

The present invention relates to the pretreatment of plastic substratesfor the chemical plating of a metal thereon. The invention is concernedwith novel plating pretreatment bath compositions, and processes ofusing such compositions, to enhance the adhesive strength of theresultant metal-to-plastic bond in the plated substrates. The inventionaffords important practical advantages over compositions and processesheretofore known and used for similar purposes.

The successful application of metal plated polymer articles hinges, to agreat extent, on the strength of the metal-to-polymer bond. Indeed,properties such as the ability to withstand extreme changes intemperature, impact resistance, tensile strength, and many others, arestrongly related to the adhesion of the metal to the polymer substrate.

To achieve adhesion, the prior art teaches subjecting the substrate to astrongly oxidizing chromic-sulfuric acid mixture at elevatedtemperature, followed by exposure of the surface to stannous chlorideand/or palladium chloride solution which prepares the polymer forsubsequent catalytic deposition of nickel, copper, cobalt or'othersuitable conductive metallic coatings that will receive an electroplatewhen suitably immersed in an electrolytic plating bath. The articlesthus obtained consist of plastic-metal composites in which the metalliccoating may vary from less than 0.1 mil to as high as 2.0 mils or morein thickness.

Certain limitations are inherent in this prior art teaching which can besummarized as follows:

1. Only specially compounded plastics can be treated to give adequateadhesion. One such plastic is ABS (acrilonitrile-butadiene-styrene), andit accounts for the majority of metal plated plastic articles in use atthis time.

2. Even on ABS, the earlier method affords relatively low adhesionvalues that limit application to functional parts which are not requiredto undergo extreme temperature variation in use.

'3.. The earlier method requires carefully molded,

stress-free plastic articles, otherwise adhesion failures due tostressed areas are difficult to overcome.

4. ABS, because it requires special and careful formulation, isrelatively expensive compared to other available polymers, especiallypolyolefins.

In order to prepare polymers other than ABS for subsequent metaldeposition, methods more recently developed involve subjecting theplastic to certain unsaturated organic solvents, oils, acids, etc.,which are retained by the surface of the substrate and facilitatesubsequent penetration by the usual chromic-sulfuric etching solution,giving substantial improvement in platability. While the exact nature ofthis surface impregnation by the organic solvent or adhesion promoter asit is hereinafter referred to is not fully understood, variouspostulations have been advanced. In US. Pat. No. 3,556,955, there aredisclosed compositions and processes for conditioning plastic substratessuch as polypropylene by the use of some 'of these orpromoters includehighly unsaturated fatty acids, e.g., sorbic acid, linoleic acid,linolenic acid, elacostearic acid and liconic acid and their esters,amides and imides; the amides and imides of mono-unsaturated fatty acidssuch as oleic and ricinoleicacid; also highly unsaturated aliphatichydrocarbons such as aqualene; highly unsaturated alicyclic compoundssuch as abietic acid; aliphatic polyethers such as polyethylene glycol,polypropylene glycol, as well as their adducts and esters, as-forexample, the poly(ethylene oxide) adducts of nonyl phenol; tertiaryaliphatic compounds such as isobutyric and isovaleric acid and theesters, amides and imides thereof; and the aliphatic substitutedaromatic compounds containing at least one benzylic hydrogen such ascumene, thymol and their derivatives. These compounds may be employed intheir more or less natural or crude form, for example by direct use ofsuch products as castor, linseed, tall or tung oil, wood rosin and thelike.

The procedures described in the aforesaid prior patent involve bothincorporation of the adhesion promoters directly in the resincompositions during compounding, as well as impregnation of the surfaceof the resin compositions after molding into finished products.impregnation of the surface of finished molded products in accordancewith the method disclosed in said prior patent involves the immersion ofthose products in a bath of one or more of the aforesaid promoters, forexample castor, linseed or tung oil at appropriate temperatures and forsuitable times. It is conganic adhesion promoters. Examples of thesejectured that the resulting increase in adhesive strength of themetal-to-plastic bond is obtained as the result of providing on or inthe surface of the plastic fractions or remnants of the organic promotermaterials which after the pretreated substrate has been subjected to anoxidation step, provide carboxyl-containing free radicals attached tothe polymer molecule and it is these which serve to link the metal tothe plastic.

For practical commercial applications it is considered necessary thatthe adhesion or minimum peel strength of a metal-to-plastic composite beon the order of at least 5 pounds per inch between the plated depositand the substrate; generally three to five times that value is desired.When organic adhesion promoters such as those described above are usedin their more or less natural state, as is disclosed in the aforesaidprior application, it is necessary, in order that effective peelstrength in the metal-plastic composite be obtained, that thetemperatures of such promoters be maintained at substantially elevatedlevels, generally on the order of at least 250 to 275 F. While thisgives effective results from a bonding standpoint, there are manyinstances in which the molded plastic product undergoing plating is ofcomplex configuration involving both relatively thick and relativelythin sections of plastic, indentations, pockets or recesses, as well asplanar and curvilinear sections. As a result, substantial internalstresses can be and are relieved upon immersing the articles in the hotbath for the substantial periods of time needed. Generally periods of 3minutes or more are required to be effective. Warping, sinking or otherdistortion of the parts frequently are encountered as 'a consequence ofrelaxing strains.

or relieving-these internal There are, in addition, other seriousdifficulties that limit the applicability of these organic solvents,oils, acids, etc., as adhesion promoters for commercial use as it hasheretofore been proposed to use them. Given below are a few of thedifficulties encountered.

1. These organic promoters are generally quite flammable and present adefinite fire hazard.

2. The prior method of use of these organic adhesion promoters, coupledwith the elevated temperatures which they require for adequate surfacetreatment of the plastic polymer, causes excessive evaporation andrequires special ventilation precautions to protect operating personnel.

3. The prior method of use further requires reracking of the partsbecause these organic agents under the conditions employed tend tosoften and damage the Plastisol coating conventionally used on thearticle transporting racks, and makes plating of the articles in asingle, continuous step-wise sequence difficult or impossible, andincreases processing costs.

4. The prior method of use of these organic solvents and especially thehighly viscous oils such as castor, linseed or tung oil, causesexcessive retention or drag-out by the articles being treated, andnecessitates the use of a second organic solvent dip to remove theexcess of organic promoter from the surface, blind holes, recesses,etc., of the parts before plating.

5. The parts must be cooled to approximately room temperature prior toremoving excess oil in the solvent. This necessitates an increase inproduction time.

It is one of the principal objectives of the present invention toprovide organic adhesion promoter compositions and processes which areeffective at substantially lower operating temperatures and whichtherefore do not give rise to relaxation of internal stress andsubsequent warping or deformation of the plastic parts.

Another major objective of the invention is improvement in operating orprocessing steps whereby reracking of the plastic articles between theadhesion promoter impregnating step and subsequent pretreatment andplating operations is avoided, thus affording greater simplification ofprocessing operations with resulting economies in the handling of theparts to be plated.

Other objectives include the reduction of evaporation losses,simplification of ventilation requirements, substantial reduction oftire hazard and other advantages flowing from these, as will becomeapparent hereinafter.

In accordance with the present invention, these ob jectives are achievedby the use of many of the same adhesion promoting compositions of theorganic solvent, oil, acid, etc., type heretofore proposed as well asother similar low molecular weight organic highly unsaturated compounds.However, instead of using those compounds in their normal state,'i.e.,as a single-phase solution, they are prepared and used in a two-phasesystem comprising very fine aqueous dispersions of these compoundsproviding stable emulsions or microemulsions of the oil-in-water type.By using these emulsions in the adhesion promoting bath in place of thesingle-phase solutions heretofore proposed, the bath temperature may bereduced to a wholly unexpected degree, usually by at least as much as100 F, so that the in any event seriously operating temperature of thebath is below the boiling point of water and in many cases is as low as135 to 155 F.

Without intending to be bound by an explanation of the theory ormechanism responsible for this dramatic I decrease in practicaloperating temperatures, it is postulated that this occurs because of thevery high surface energy which results from low interfacial surfacetension and enormous surface areas of the agent particles in theemulsion system. The heat of wetting is thus increased tremendously,providing increased adhesion of the particles to the substrate andgreatly increased rate of diffusion of such agent particles intomicroscopic or submicroscopic pores of the polymer. ln fact, visualevidence of this diffusion is supplied by incorporating a dye into theorganic promoter agent of the emulsion system, which dye can then beobserved to penetrate substantially into the plastic material itselfupon immersing it in the bath.

Numerous other advantages apart from lower temperature operations arealso realized by the present invention. Using the organic adhesionpromoting agent in the form of a fine disperson or emulsion, the amountof agent needed to effect the desired adhesion properties in the plasticcan be reduced to as little as 10 to 15 percent by volume of the totaltreatment solution in contrast to the percent heretofore used. This inturn substantially reduces fire hazards, ventilation problems to removefumes that could not be tolerated by operating personnel, evaporationlosses, and affords lower costs. Most importantly, by using the emulsionsystem it no longer is necessary to re-rack articles when transportingthem from the adhesion promoting bath to subsequent preconditioning andplating baths, since the adherent solution from the novel adhesionpromoting bathcan be easily rinsed in plain water and since the bath nolonger adversely affects the Plastisol coating on the racks. Thus theinvention makes it possible to provide a truly continuous plasticplating process in which the articles are transported by the same racksuccessively through each of the various preconditioning and platingbaths without interruption from start to finish.

The invention is illustrated by the following examples which are givenby way of explanation of the concept involved and its application topractical plastic plating applications. The examples are not intended tobe allencompassing of the invention since it will be readily apparent tothose skilled in the art that the teaching herein provided may beapplied to produce equivalent substitute compositions. The appendedclaims are accordingly intended to cover not only the specific exampleshere given but their lawful equivalents.

EXAMPLE l a. Linseed oil b. Steam distilled wood turpentine c. Linoleicacid 3 grams 3 grams 1.5 grams 7 d. Surfactant 2% by volume sufficientto make 300 mls. total solution to bring solution to neutral or slightlyalkaline pH e.g., about 7 to 9) e. Water f. Potassium hydroxideSurfactants such as lGEPAL C0630 and C0730, in substantially equalamounts, are satisfactory. These are non-ionic emulisfying agentsproduced commercially where R is C H or a higher homolog.

The preparation of the foregoing emulsion is accomplished as follows: 20grams of linseed oil, 20 grams of turpentine and 10 grams of linoleicacid are mixed with 20 mls. each of IGEPAL C0730 and C0630, heated toabout 120 F and 100 mls. of water added with constant stirring. A 10percent solution of potassium hydroxide is then added until the pH ofthe solution is about 8.0. Thereafter, additional water is added withconstant stirring to give a total volume of 300 mls. This is aconcentrated solutionand from this the adhesion promoting bath describedin the above example is prepared by diluting with additional water sothat the concentrate constitutes about 15 percent by volume of the finaltotal solution.

Following the adhesion promoting bath, the treated plastic bezel is runthrough a cold water rinse and then immersed in a chromic-sulfuric acidoxidizing solution consisting of approximately 30 percent by weightchromic acid, 25 percent by weight sulfuric acid (66Be), the balancebeing water. This solution has a specific-gravity of approximately 1.48at a temperature of 170 F and the substrate is held in the solution fora period of about minutes.

The etched substrate is then thoroughly rinsed by a double'cold waterrinse and is next immersed in a solution of phosphoric acid (40-45percent by volume) containing -20 parts per million of lGEPAL C0630 at atemperature of 80 F. After about 5 minutes soaking in this solution,the' bezel is again rinsed in cold water and transferred to anactivating solution prepared as follows:

Components Nos. 1, 2, and 3 in 'the above composition are mixed at roomtemperature until all of the palladium chloride is dissolved. The firstportion of stannous chloride (component No. 4) is then added and theresulting solution stirred for 10 minutes. Components Nos. 5, 6, and 7are mixed separately from the foregoing and the first solution is thenpoured into this second solution with constant stirring. All preparationis done at room temperature. The resulting concentrated activatorsolution is then heated for about 3 hours at about 150 F and thendiluted for use in the activating bath. In general it is satisfactory touse about 10 to 20 percent by volume of the aforesaid concentrate, 20percent by volume of concentrated hydrochloric acid, the balance beingwater.

This activating bath is used at F and the bezel is retained in it forabout 5 minutes. Thereafter, the bezel is removed and then again rinsedin cold water and subjected to a leaching or accelerating stepcomprising immersing it in an aqueous solution of fluoboric acid at aconcentration of about 2 pounds per gallon at a temperature of 1 10 Ffor 1 minute.

Again the bezel is thoroughly rinsed in cold water and immersed in anelectroless plating solution. Any number of conventional copper ornickel electroless plating compositions can be used in this step, butfor nickel plating a particularly suitable system is described in U.S.Pat. No. 2,532,283,. Example V, Table 1. Similarly, a highly suitablecopper solution is disclosed in U.S. Pat. No. 3,095,309, Example 1.Electroless plating is then followed by electroplating in conventionalmanner.

The resulting plate shows uniform coverage and good adhesion in whichthe minimum peel strength is about 15 pounds per inch.

EXAMPLE ll Again, a molded polypropylene article was washed and thenplaced in an adhesion promoting aqueous emulsion of the followingcomposition:

22 mls.

f. potassium hydroxide to being the solution to neutral or slightlyalkaline pH The surfactants used here were IGEPAL C0630 and TRITON X-l00in equal amounts. TRITON X-l00 is the trade name of Rohm & Haas forsurfactants of the alkylarly polyether alcohol water soluble type.

The foregoing emulsion is prepared by heating the water to about F,adding the potassium hydroxide (about 38 grams per liter) and stirringuntil dissolved, after which the previously mixed linseed oil, oleicacid, turpentine and surfactants are added and stirred in.

The plastic article is retained in the adhesion promoter for about 15minutes at a solution temperature of F. Thereafter, the article isprocessed through the balance of the steps outlined in Example I. Theadhesion obtained from this procedure varies between 15 and 24 poundsper inch on unaged parts.

While useful, the particular adhesion promoting emul-' EXAMPLE "I Theprocedure is the same as in Example 1 except that the following emulsionis substituted for the adhesion promoter of that example:

40 mls. 60 mls.

a. turpentine b. surfactants c. water 900 mls.

ln this formulation, a mixture of water soluble surfactants consistingof 50 mls. IGEPAL C0630 and 10 mls. of BENAX 2A1 is especially suitableBENAX 2A1 is the trade designation of Dow Chemical Co. for sodiumdodecyl diphenyl ether disulfonate and is used in the foregoingformulation primarily to prevent clouding of the solution, particularlyat the temperature of use. This formulation of adhesion promoter isparticularly stable at all temperatures up to and including normal bathoperation temperature of from 145 to 155 F. [mmersion periods for theparts at this operating temperature range is 10 to minutes.Polypropylene parts treated in this bath, followed by the remainder ofthe plating cycle steps outlined in Example 1, show peel or bondstrengths of 25 pounds per inch, or more.

Other promoters such as castor oil, tung oil and tall oil all exhibitsimilar adhesion improving qualities when used in the form of aqueousoil-in-water emulsions similar to those of the foregoing examples.Accordingly it appears that any of the adhesion promoters of the typesdisclosed in the aforesaid U.S. Pat. No. 3,556,955 can be successfullyused in the form of aqueous emulsions. For economic reasons, as well asease of handling, the pine derivatives such as turpentine are presentlypreferred.

As has been pointed out above, the effectiveness of the emulsions inpromoting surface modification of the plastic substrates is believed tobe due to the tremendous surface energy made available by using theactive adhesion promoting agent in finely divided or dispersedcondition. The emulsions described in the foregoing examples show a veryhigh order ofdispersion. Those of Examples I and II are at leastmacro-emulsions whose active particle sizes are on the order of one-halfto a maximum of about fifty microns. The particle sizes in Example 111appear to be more accurately described as micro-emulsions whose sizerange from 50 to 500 angstroms. The. benefits of the invention inrespect to lower operating temperatures, lower concentrations, equipmentand process simplification, etc., are accordingly believed to be thedirect result of employing the active agent in colloidal, highlydispersed form.

What is claimed is:

l. The process of increasing the adhesion of plated metal onpolypropylene substrates, which comprises immersing the substratein'aqueous emulsion of an organic latent adhesion promoter consistingessentially a. linseed oil 3 grams b. turpentine 3 grams c. linoleicacid 1.5 grams d. surfactant 2 b volume e. deionized water to ma e 300mls. total solution a. linseed oil 22 mls. b. turpentine 22 mls. c.oleic acid 1 l mls. d. surfactant 44 mls. e. water 900 mls.

f. potassium hydroxide to provide about 38 grams per liter of finalemulsion.

4. The process defined in claim 3, wherein the substrate is immersed insaid emulsion for a period of about 10 minutes at a temperature of 175F.

.5. The process defined in claim 1, wherein said adhesion promoter is anaqueous emulsion consisting essentially of:

a. turpentine 44 mls. b. surfactant 60 mls. c. water 900 mls.

6. The process defined in claim 5, wherein the substrate is immersed insaid emulsion for a period of 10 to 15 minutes at a temperature of to F.

7. The method of plating a polystyrene substrate with a metal film bychemical deposition from an aqueous solution containing a soluble saltof the metal to be deposited, which comprises the steps of a. cleaningthe surface of the resin substrate by immersing it in a hot aqueousalkaline solution;

b. withdrawing the substrate from said cleaning solution and immersingit in the aqueous adhesion promoting emulsion consisting essentially of:

a. linseed oil 3 grams b. turpentine 3 grams c. linoleic acid 1.5 gramsd. surfactant 2% by volume e. water to make 300 mls. total solution f.potassium hydroxide to give a pH of about 8,

for a period of about 10 minutes at a temperature of approximately F;

rinsing the substrate and immersing it in a chromic-sulfuric acidoxidizing solution consisting essentially of about 30 percent(weight)chromic acid, 25 percent (weight) sulfuric acid (66 Be), thebalance being water, maintaining said substrate in said oxidizingsolution while at a temperature of about 170 F for 5 minutes;

. removing and thoroughly rinsing said substrate in water, thenimmersing it in an aqueous solution of phosphoric acid containing 10-20ppm of a surface active agent for about 5 minutes;

. removing and rinsing the substrate in water and then immersing it in acolloidal activating solution comprising about 20 percent (volume) ofconcentrated hydrochloric acid, 60-70-percent (volume) water and from10-20 percent (volume) of the following composition:

PdCl, 0.16 l-lCl (37%) 58.0 Water (deionized) 33.9 SnCl, (anhydrous)6.82 Na,SnO, ll-1,0 1.13

and maintaining said substrate in said activating solu tion for about 5minutes at 80F;

f. removing said substrate, rinsing in water and then b. oleic acid itmls. immersing it in an aqueous accelerating solution c-mrvemine 22 d.surfactants 44 mls. containing approximately 2 pounds of fluorobonc watrv 900 mm acid per gallon for 1 minute at 1 10 F; f. potassium hydroxide38 grams. g. removing andrinsing the substrate and immersing 5 it in anaqueous electroless copper or nickel plat- 9. The method as defined inclaim 7, except that in mg Solution to deposit adhere"! film 0f the step(b) thereof said substrate is immersed in an aquemfital SaidSubstrateous adhesion promoting emulsion consisting essentially 8. Themethod as defined in claim 7, eiicept that in f; step (b) thereof saidsubstrate is immersed in an aquel0 ous adhesion promoting emulsionconsisting essentially turpentine I 40 mls.

of: b. surfactant 60 mls. c. water 4 900 mls.

a. linseed oil 22mls.

1. The process of increasing the adhesion of plated metal onpolypropylene substrates, which comprises immersing the substrate inaqueous emulsion of an organic latent adhesion promoter consistingessentially of: a. linseed oil 3 grams b. turpentine 3 grams c. linoleicacid 1.5 grams d. surfactant 2 % by volume e. deionized water to make300 mls. total solution f. potassium hydroxide to give a pH of about 8.0then oxidizing the resulting substrate to develop said adhesionpromoter, and thereafter plating the oxidized substrate.
 2. The processdefined in claim 1, wherein the substrate is immersed in said emulsionfor a period of about 10 minutes at a temperature of 170* F.
 3. Theprocess defined in claim 1, wherein said adhesion promoter is an aqueousemulsion consisting essentially of: a. linseed oil 22 mls. b. turpentine22 mls. c. oleic acid 11 mls. d. surfactant 44 mls. e. water 900 mls. f.potassium hydroxide to provide about 38 grams per liter of finalemulsion.
 4. The process defined in claim 3, wherein the substrate isimmersed in said emulsion for a period of about 10 minutes at atemperature of 175* F.
 5. The process defined in claim 1, wherein saidadhesion promoter is an aqueous emulsion consisting essentially of: a.turpentine 44 mls. b. surfactant 60 mls. c. water 900 mls.
 6. Theprocess defined in claim 5, wherein the substrate is immersed in saidemulsion for a period of 10 to 15 minutes at a temperature of 145* to155* F.
 7. The method of plating a polystyrene substrate with a metalfilm by chemical deposition from an aqueous solution containing asoluble salt of the metal to be deposited, which comprises the steps ofa. cleaning the surface of the resin substrate by immersing it in a hotaqueous alkaline solution; b. withdrawing the substrate from saidcleaning solution and immersing it in the aqueous adhesion promotingemulsion consisting essentially of: a. linseed oil 3 grams b. turpentine3 grams c. linoleic acid 1.5 grams d. surfactant 2% by volume e. waterto make 300 mls. total solution f. potassium hydroxide to give a pH ofabout 8, for a period of about 10 minutes at a temperature ofapproximately 170* F; c. rinsing the substrate and immersing it in achromic-sulfuric acid oxidizing solution consisting essentially of about30 percent (weight) chromic acid, 25 percent (weight) sulfuric acid (66*Be), the balance being water, maintaining said substrate in saidoxidizing solution while at a temperature of about 170* F for 5 minutes;d. removing and thoroughly rinsing said substrate in water, thenimmersing it in an aqueous solution of phosphoric acid containing 10-20ppm of a surface active agent for about 5 minutes; e. removing andrinsing the substrate in water and then immersing it in a colloidalactivating solution comprising about 20 percent (volume) of concentratedhydrochloric acid, 60-70 percent (volume) water and from 10-20 percent(volume) of the following composition: Wt. % PdCl2 0.16 HCl (37%) 58.0Water (deionized) 33.9 SnCl2 (anhydrous) 6.82 Na2SnO3 .3H2O 1.13 andmaintaining said substrate in said activating solution for about 5minutes at 80* F; f. removing said substrate, rinsing in water and thenimmersing it in an aqueous accelerating solution containingapproximAtely 2 pounds of fluoroboric acid per gallon for 1 minute at110* F; g. removing and rinsing the substrate and immersing it in anaqueous electroless copper or nickel plating solution to deposit anadherent film of the metal on said substrate.
 8. The method as definedin claim 7, except that in step (b) thereof said substrate is immersedin an aqueous adhesion promoting emulsion consisting essentially of: a.linseed oil 22 mls. b. oleic acid 11 mls. c. turpentine 22 mls. d.surfactants 44 mls. e. water 900 mls. f. potassium hydroxide 38 grams.